linux-kernel - Re: [PATCH 2/4] arch/arm: move secure

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Date:	Fri, 9 Nov 2012 11:56:08 +0000
From:	Will Deacon <will.deacon@....com>
To:	Kees Cook <keescook@...omium.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>,
	Geremy Condra <gcondra@...gle.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Will Drewry <wad@...omium.org>
Subject: Re: [PATCH 2/4] arch/arm: move secure_computing into trace

One really minor nit...

On Thu, Nov 08, 2012 at 08:59:31PM +0000, Kees Cook wrote:
> There is very little difference in the TIF_SECCOMP and TIF_SYSCALL_WORK
> path in entry-common.S, so merge TIF_SECCOMP into TIF_SYSCALL_WORK and
> move seccomp into the syscall_trace_enter() handler.
> 
> Expanded some of the tracehook logic into the callers to make this code
> more readable. Since tracehook needs to do register changing, this portion
> is best left in its own function instead of copy/pasting into the callers.
> 
> Additionally, the return value for secure_computing() is now checked
> and a -1 value will result in the system call being skipped.
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>

[...]

> @@ -944,19 +939,39 @@ static int ptrace_syscall_trace(struct pt_regs *regs, int scno,
>  
>  asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
>  {
> -	scno = ptrace_syscall_trace(regs, scno, PTRACE_SYSCALL_ENTER);
> +	current_thread_info()->syscall = scno;
> +
> +	/* do the secure computing check first */
> +	if (secure_computing(scno) == -1) {
> +		/* seccomp failures shouldn't expose any additional code. */
> +		scno = -1;
> +		goto out;
> +	}

Can we just return -1 here instead please? The whole jump label code makes
this code messier than it needs to be and there's no cleanup to be done.

> +	if (test_thread_flag(TIF_SYSCALL_TRACE))
> +		scno = tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
> +
>  	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
>  		trace_sys_enter(regs, scno);
> +
>  	audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0, regs->ARM_r1,
>  			    regs->ARM_r2, regs->ARM_r3);
> +
> +out:
>  	return scno;
>  }

Cheers,

Will

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